BURLINGAME — Hospital watchdog group Peninsula Guardians has dropped part of its lawsuit regarding the new Peninsula Medical Center to focus on what they say is an illegal 50-year lease agreement between the Peninsula Health Care District and Mills-Peninsula Health Services.

Guardians attorney Mitchell Green said Wednesday that the group dropped the San Mateo County Elections Office from its lawsuit because the election “is moot at this point.”

“The core issue of the litigation is about whether they can go out to 50 years for this lease and we maintain that they cannot,” Green said.

Mills-Peninsula on Wednesday, meanwhile, filed a demurrer with the San Mateo County Superior Court in response to the suit, saying that the lease agreement is legal. Mills-Peninsula attorney Harriet Steiner said in the document that a 30-year limit on such leases cited by the Guardians does not apply, in part because the District is not leasing an existing hospital to the organization.

Mills-Peninsula plans to build a $488 million hospital at its own expense that will meet 2013 state-mandated seismic safety standards. Mills-Peninsula will pay the District, which is the landowner, $1.5 million in annual rent in the next 50 years, after which the District plans on buying back the hospital.

In August, an overwhelming majority of 101,000 District voters approved Measure V — a special mail-in ballot vote that sought the public’s OK for a new Peninsula Medical Center, located at 1783 El Camino Real.

Peninsula Guardians, a nonprofit watchdog formed in response to the hospital project, first filed a lawsuit against the County Elections Office, Mills-Peninsula and the District.

District attorney Doug Straus said he also will likely file a demurrer with the court, asserting that the Guardians’ complaint does not have legal grounding, nor does it present a way to fix the perceived problem.

A case management conference for the lawsuit is scheduled for Dec. 6, according to San Mateo County Superior Court records.